Japanese Unexamined Patent Application Publication No. H9-225724 (Patent Document 1) discloses an example of a conventional tip that can be used as a cutting insert in a process for machining a workpiece. The tip disclosed in Patent Document 1 includes a plurality of cutting edges that have a circular arc shape when viewed from the side and have a curved shape that protrudes outwards when viewed from directly above. With this cutting edge configuration, when the cutting edge is brought into contact with the workpiece, the portion of the cutting edge that has the greatest height contacts the workpiece first, and shorter portions of the cutting edge contact the workpiece gradually. This makes it possible to reduce the impact force on the tip.
As illustrated in FIGS. 16 and 17, when a cutting edge 309 has a curved shape that protrudes outwards when viewed from directly above like the circular arc-shaped cutting edge disclosed in Patent Document 1, the thickness R1 of chips cut from a workpiece 201 by a region of the cutting edge near an end portion that contacts the bottom machining surface 201a of the workpiece 201 (hereinafter, referred to as a first region 309a) is less than the thickness R2 of chips cut from the workpiece 201 by a region of the cutting edge farther away from the end portion (hereinafter, referred to as a second region 309b). Therefore, a relatively large force is applied to the second region 309b. 
Meanwhile, in the tip disclosed in Patent Document 1, the cutting edge 309 has a circular arc shape and is therefore bilaterally symmetric about the center of the cutting edge, which has the greatest height. As a result, even if the first region 309a cuts the workpiece 201 in a satisfactory manner, the inclination of the cutting edge 309 is insufficient in the second region 309b. This makes it more difficult for the second region 309b to cut the workpiece 201 in a satisfactory manner.
The present invention was made in view of the above-mentioned problems and aims to provide a cutting insert having satisfactory cutting ability even when the cutting edge has a curved shaped that protrudes outwards when viewed from directly above, as well as a cutting tool and a method for manufacturing a cut product.